As far as my (limited) understanding goes, all elements will give off light. However, the work function of elements are varied and so it will be much easier to stimulate electrons in some metals than others.

I have to add, we only quickly covered this topic in class last week, I could be completely wrong.

I believe that all elements emit visible photons, although of course there are other photons emitted that are not visible to our eyes (e.g. infra red, ultra violet).

I'm not sure what your last question is saying, but if you are asking if it's a bit of a coincidence that elements give off light that we can see, then I think the truth is the other way around. We have evolved to detect the kind of photons that are most prevalent in our environment. If there was a larger proportion of, say, UV photons in our environment, we would probably have evolved to be able to see them, and would perhaps not be able to see red, in the same way that we can't see infra red.

Elements only give off light when a transition occurs. An electron can be excited by absorbing energy, then when it moves back down an energy level, release the energy as a photon of light. It is mostly metals that give of distinctive colours (such as Sodium) because they have fewer possibly energy states, so more photons released are likely to have the same energy, and therefore the same wavelength. Elements with more possible energy levels give off photons with a range of wavelengths, therefore the colour is less distinctive. As far as I know, all elements have emission spectra.
Humans are made up of thousands of different complex molecules. Elements only give off light when heated (or given energy). Humans would have to be heated (possibly quite a lot), and different elements within the human would take different amounts of energy to excite the electrons, which would then release photons at a range of wavelengths, so you wouldn't really be able to see anything, as the most distinctive coloured emission spectra of metals only occur in trace amounts in the body. Not a great experiment pratically-wise :P